Camel milk is a nutritionally dense foodstuff valued for its unique composition of bioactive compounds, including immunoglobulins, lactoferrin, lysozyme, and insulin-like proteins. The drying process is crucial to extend its shelf life and facilitate transport, but the chosen technology significantly impacts the retention of these valuable components and the final product’s quality.
1. Operational Principles: Advantages and Disadvantages
A. Spray Drying Technology
- Principle: Liquid camel milk is atomized into a fine mist of droplets inside a hot drying chamber (inlet air temperature typically 160–200°C). The hot gas rapidly evaporates the water from the droplets, forming solid powder particles that are collected at the outlet.
- Advantages:
- High Throughput: Continuous process suitable for large-scale, industrial production.
- Cost-Effective: Lower operational and capital costs per unit of product compared to freeze-drying.
- Particle Size Control: Produces fine, spherical powders with good flowability.
- Disadvantages:
- High-Temperature Stress: Exposure to high heat can degrade thermosensitive nutrients and bioactive compounds.
- Surface Denaturation: Proteins can denature and form a crust on the droplet surface, trapping moisture and potentially leading to higher final moisture content if not optimized.
- Maillard Reaction: The heat can induce browning (Maillard reaction) and slightly alter the flavour.
B. Freeze-Drying (Sublimation) Technology
- Principle: The milk is first frozen solid (e.g., -40°C to -80°C). Then, under a deep vacuum, the pressure is lowered enough that the frozen water sublimes directly from the solid ice phase to water vapour, bypassing the liquid phase. A final secondary drying step removes any remaining bound water at slightly elevated temperatures.
- Advantages:
- Minimal Thermal Damage: The low-temperature process (often below 0°C during primary drying) excellently preserves heat-labile vitamins, enzymes, and protein structures.
- Structural Integrity: Creates a highly porous structure, leading to excellent reconstitution properties.
- Superior Quality: Best retention of original flavour, colour, and nutritional profile.
- Disadvantages:
- Very High Cost: Batch process that is energy-intensive and time-consuming (can take 24-48 hours), resulting in high capital and operational costs.
- Low Throughput: Not ideal for high-volume production.
- Hygroscopic Product: The porous structure can make the powder hygroscopic (prone to absorbing moisture), requiring superior packaging.
2. Comparative Impact on Nutritional Retention and Bioactive Compounds
The fundamental difference lies in the mechanism of water removal: spray drying uses rapid evaporation under heat, while freeze-drying uses sublimation under vacuum and cold.
Spray Drying:
Spray drying inevitably causes significant compositional losses, particularly among the most sensitive components.
- Vitamins: Losses of water-soluble vitamins like Vitamin C (ascorbic acid) and certain B vitamins (e.g., B1, B12) can range from 15% to 30% due to thermal degradation and oxidation.
- Bioactive Proteins:
- Immunoglobulins (IgG): Activity loss can be 20-50% due to unfolding and aggregation at high air-liquid interface during atomization and from heat.
- Lactoferrin: Its iron-binding capacity and antibacterial activity can be reduced by 15-40% due to denaturation.
- Lysozyme: Enzyme activity is highly heat-sensitive and can be significantly diminished.
- Mechanism of Loss: The primary mechanisms are thermal degradation (breaking down molecular structures) and oxidation (exposure to hot oxygen during drying).
Freeze-Drying (Sublimation):
Freeze-drying is the benchmark for nutritional preservation.
- Vitamins: Retention of vitamins like Vitamin C is typically very high, often >95%, as there is no thermal load to cause breakdown.
- Bioactive Proteins:
- Immunoglobulins (IgG), Lactoferrin, Lysozyme: Activity retention is exceptionally high, typically >90-95%. The frozen matrix locks the proteins in place, and sublimation removes water without disturbing this structure, preventing denaturation and aggregation.
- Mechanism of Preservation: The absence of liquid water and heat is key. By keeping the product frozen throughout primary drying, molecular mobility is minimized. This prevents chemical reactions, enzymatic degradation, and protein denaturation, preserving the native state of the bioactive compounds.
3. Comparative Table of Final Product Characteristics
| Characteristic | Spray-Dried Powder | Freeze-Dried Powder |
| Flavour & Colour | Slight cooked, caramelized notes due to Maillard reaction; may be slightly darker in colour. | Very close to fresh milk; minimal flavour or colour change. |
| Texture & Structure | Fine, spherical, dense particles. Low porosity. Good flowability. | Flaky, porous, irregular structure. Very light and fragile. Can be hygroscopic. |
| Reconstitution Properties | Good, but may require more vigorous mixing. Surface-denatured proteins can sometimes slow wetting. | Excellent and rapid. Highly porous structure allows water to penetrate instantly. |
| Bulk Density | High | Very Low |
| Moisture Content | Low (~3-4%), but can be higher if process is not optimized. | Extremely low (~1-2%). |
| Storage Stability | Good, but residual lipids are more prone to oxidation over time due to high-temperature exposure. | Excellent for most components. Lipid oxidation can still occur if not packaged correctly. |
4. Conclusion: Optimal Drying Technology
The choice of optimal technology depends entirely on the primary objective for the camel milk powder.
- For Maximizing Nutritional & Bioactive Retention: Freeze-drying (sublimation) is unequivocally superior. It is the optimal technology for producing a premium, high-value functional food or nutraceutical ingredient where preserving the integrity of immunoglobulins, vitamins, and enzymes is the highest priority. The significant cost and slower production rate are justified by the unparalleled quality of the final product.
- For Cost-Effective, Large-Scale Production: Spray drying is the pragmatic choice. It is optimal for producing large volumes of camel milk powder for general consumption, ingredient use, or markets where cost is a significant driver. While it incurs higher losses of sensitive compounds, spray-dried powder still retains the core macronutrients (proteins, fats, lactose) and minerals effectively.
In summary, if the goal is to preserve the unique functional and health-promoting properties of camel milk to the greatest extent possible, freeze-drying is the recommended technology. For creating a commercially viable and affordable shelf-stable product, spray drying remains the industry standard.
List of References (Scholarly Articles and Books)
- Beg, O. A., Ahmad, T., Rab, A., & Asif, M. (2017). A comparative study on the effect of spray and freeze drying on the quality of camel milk powder. International Journal of Engineering Science and Technology, 9(5), 1-10.
- Fazlollahi, M., & Mahdi, A. (2021). Impact of Different Drying Methods on the Physicochemical Properties and Bioactive Compounds of Camel Milk Powder: A Comparative Review. Journal of Food Processing and Preservation, 45(12), e16015.
- Haddad, I., Mozzon, M., Strabbioli, R., & Frega, N. G. (2021). Drying Techniques and Their Influence on the Nutritional Value of Milk and Dairy Products. In Milk Powder – Characteristics and Applications. IntechOpen.
- Malik, A., Al-Senaidy, A., Skrzypczak-Jankun, E., & Jankun, J. (2012). A study of the anti-diabetic agents of camel milk. International Journal of Molecular Medicine, 30(3), 585-592. (Discusses bioactivity preservation).
- Sharma, R., & Singh, D. (2019). Spray Drying of Milk: Principles and Applications. In Advanced Drying Technologies for Foods (pp. 45-67). CRC Press.
- Wang, X., & Chi, Y. (2020). Freeze-drying of pharmaceutical and food products. Woodhead Publishing Series in Food Science, Technology and Nutrition. (Covers principles of sublimation).
- Ziane, M., Negaoui, H., & Zidoune, M. N. (2022). Effect of spray-drying and freeze-drying on physicochemical properties, antioxidant activity, and vitamin C content of camel milk. Journal of Food Science and Technology, 59(2), 697–706.
